Control unit and lighting apparatus including light engine and control unit

ABSTRACT

A LED based lighting apparatus is disclosed. The light engine used in the lighting apparatus may use printed circuit board and have a plurality of LED groups that are independently controllable by a control unit. The power supply input and return paths connected to each LED group may be implemented on different layers to allow a compact footprint that may be used with traditional fluorescent encasements with relatively little modification. The LEDs may comprise a subset of LEDs having a first colour and a subset of LEDs having a second colour different from said first colour intertwined on the light engine.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of and claims the benefit under 35 USC 120 of U.S. patent application Ser. No. 15/136,599 entitled “LED LIGHTING APPARATUS WITH FIRST AND SECOND COLOOUR LEDS” by Briggs filed on Apr. 22, 2016, which claims the benefit under 35 USC 120 of U.S. patent application Ser. No. 14/606,013 entitled “MODULAR LED STRIP LIGHTING APPARATUS” by Briggs filed on Jan. 26, 2015, which claims the benefit under 35 USC 120 of U.S. patent application Ser. No. 13/423,142 entitled “MODULAR LED STRIP LIGHTING APPARATUS” by Briggs filed on Mar. 16, 2012 which claims the benefit under 35 USC 119(e) of U.S. Provisional Patent Application 61/467,914 filed on Mar. 25, 2011 and hereby incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates generally to a lighting apparatus, and more particularly to a control unit and a lighting apparatus including a light engine and a control unit.

BACKGROUND OF THE INVENTION

Fluorescent lighting systems are widely used and many fluorescent lighting systems are designed to accommodate long slender fluorescent tubes.

Recently, lighting systems employing light emitting diodes (LEDs) have increased in popularity. LED based lighting systems may be more efficient, have a longer lifespan, and be more controllable (e.g. colour, colour temperature) compared to traditional fluorescent lighting systems. However, many existing LED based lighting systems generate a relatively large amount of heat and certain LED based lighting systems require a large number of LEDs to achieve a desired lumen output. These factors may limit the layout of LEDs in LED based lighting systems and make it relatively difficult to modify the encasements used in fluorescent lighting systems for use with LEDs.

The present invention aims to mitigate at least one of the shortcomings of prior art lighting systems.

SUMMARY OF THE INVENTION

In an embodiment of the invention there is provided a lighting apparatus comprising: a light engine and a control unit. The light engine comprises: a printed circuit board; and a plurality of LED groups on said printed circuit board coupled between a power supply input and a respective one of a plurality of return paths associated with said LED group. Each of said LED groups comprises at least one LED set comprising a plurality of LEDs coupled in series. A first one of said LED groups is comprised of at least a subset of LEDs having a first colour temperature, and a second one of said LED groups is comprised of at least a subset of LEDs having a second colour temperature different from said first colour temperature. The control unit is coupled between said light engine and a power source having a power supply output coupled to said power supply input of said light engine and a power supply return. Said control unit comprises: a plurality of transistors, one of said plurality of transistors coupled between each of said return paths and said power supply return; and a controller operable to selectively activate each of said transistors to allow current to flow from said power supply output through said associated LED group to said power supply return.

In another embodiment there is provided a lighting apparatus comprising: a plurality of light engines and a control unit. Each of said light engines comprises: a printed circuit board; and a plurality of LED groups on said printed circuit board coupled between a power supply input and a respective one of a plurality of return paths associated with said LED group across said plurality of light engines. Each of said LED groups comprises at least one LED set comprising a plurality of LEDs coupled in series. A first one of said LED groups is comprised of at least a subset of LEDs having a first colour temperature, and a second one of said LED groups is comprised of at least a subset of LEDs having a second colour temperature different from said first colour temperature. The control unit is coupled between said plurality of light engines and a power source having a power supply output coupled to said power supply inputs of each of said light engines and a power supply return. Said control unit comprises: a plurality of transistors, one of said plurality of transistors coupled between each of said return paths and said power supply return; and a controller operable to selectively activate each of said transistors to allow current to flow from said power supply output through said associated LED group on each of said plurality of light engines to said power supply return.

In another embodiment of the invention there is provided a control unit, adapted to be coupled to a light engine comprising a plurality of LED groups coupled between a power supply input and a respective one of a plurality of return paths associated with said LED group. A first one of said LED groups is comprised of at least a subset of LEDs having a first colour temperature, and a second one of said LED groups is comprised of at least a subset of LEDs having a second colour temperature different from said first colour temperature. Said controller comprises: a plurality of transistors; one of said plurality of transistors coupled between each of said return paths and a power supply return of a power source; and a controller, coupled to said transistors, operable to selectively activate each of said transistors to allow current to flow from said power supply input through said associated LED group to said power supply return.

Other aspects and features of the present invention will become apparent to those of ordinary skill in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

In the figures which illustrate by way of example only, embodiments of the present invention,

FIG. 1 is a schematic diagram illustrating the layout of one layer of an embodiment of the invention;

FIG. 2 is a schematic diagram illustrating the layout of another layer of the embodiment of the invention shown in FIG. 1;

FIG. 3 is a schematic diagram illustrating the layout of an embodiment of a LED set in greater detail;

FIG. 4 is a schematic diagram of an alternative embodiment of a LED set;

FIG. 5 is a schematic diagram of a lighting apparatus comprised of multiple light engines;

FIG. 6 is a schematic diagram of an embodiment of a control unit in greater detail;

FIG. 7 is a schematic diagram illustrating one possible arrangement of LED groups and LED sets; and

FIG. 8 is a schematic diagram of an embodiment of a pass through board that may be used in certain embodiments of the invention.

DETAILED DESCRIPTION

The layout of LEDs in many LED based lighting systems may be limited by thermal management issues and ensuring that enough area remains to facilitate the required interconnections between LEDs where a large number of LEDs are used. Certain applications may employ metal core printed circuit boards (MCPCBs) to assist in managing the heat generated by a large number of LEDs. However, many existing designs suffer from certain shortcomings, including the ability to include a plurality of controllable LEDs in a narrow or small footprint.

A schematic diagram of one layer of an embodiment of the invention is depicted in FIG. 1. Light engine 10 may be comprised of a substrate 20, for example, a metal core printed circuit board (PCB) or another suitable thermally conductive substrate, that may have an interconnection layer 22 to facilitate the attachment and interconnection or coupling of various components in a known manner. Light engine 10 may have a power supply input 50 that may be coupled to the output of a power supply to provide a source of power to light engine 10.

Light engine 10 may have a plurality of LED sets 30, 32, 34, 36, 38, and 40 coupled between power supply input 50 and a power supply return to allow a current to flow from the power supply through the various LED sets. Each LED set may be comprised of a single LED or a plurality of LEDs that may be connected in a number of different configurations. For example, each LED set may have a plurality of LEDs connected in series between power supply input 50 and the power supply return 114 (FIG. 5) as shown in greater detail in FIGS. 3 and 4. LED sets may also have different number of LEDs, depending on, for example, the forward voltage of the LEDs included in the LED set. The number of LEDs in each LED set may be chosen so that the combined total voltage across each of the LED sets is approximately equal.

Light engine 10 may also have at least one LED group that may be independently controlled by control unit 120 (FIG. 5) in certain embodiments of the invention. Each LED group may be comprised of at least one LED set. The layout of the LED sets in a LED group may vary depending on the particular application. For example, the LED sets making up a LED group may be repeated periodically along a length of light engine 10.

For example, with reference to FIGS. 1 and 7, LED group 150 may include LED sets 30 and 38. Similarly, another LED group (not shown) may include LED sets 32 and 40. The LED sets in a LED group may be repeated along a length of light engine 10 periodically depending on the number of LED groups employed in the light engine. For example, for a light engine having a modulo M architecture with M LED groups, each LED group may include every 1/Mth LED set. With reference to FIG. 1, each LED group may include every fourth LED set as four LED groups (not specifically enumerated) may be employed.

Each LED group may have a return path associated with the LED group to complete the circuit to a power supply return 114 in order to allow a current to flow from power supply output 112 and through the LEDs of each LED group. In order to facilitate the independent control of each LED group, each LED group may have a separate return path. For example, LED group 150 may have LED sets 30 and 38 that may be coupled between power supply input 50 and return path 80. Similarly, LED sets 32 and 40 of a second LED group may be coupled to return path 82. LED sets 34 and 36 may be members of different LED groups and be coupled to return paths 84 and 86 respectively. LED sets mounted to and coupled together using interconnection layer 22 may be coupled to return paths disposed in another interconnection layer, interconnection layer 24, using layer interconnection elements, such as vias according to known methods. For example, LED sets 30 and 38 may be coupled to return path 80 using layer interconnection elements 60 and 68. Similarly, layer interconnection elements 62, 64, 66, and 70 may be employed to connect LED sets 32, 34, 36, and 40 to return paths 82, 84, 86, and 82 respectively. Generally, all LED sets in a particular LED group may be coupled to the same return path using layer interconnection elements at various points on light engine 10. Such a configuration allows the LED groups to be controlled independently as described below. Although, four return paths and LED groups are shown in light engine 10 any number of return paths and LED groups may be used, for example, eight LED groups may be used in certain applications.

One particular embodiment of LED set 30 is shown in greater detail in FIG. 3. It should be noted that numerous other configurations may also be used without departing from the scope of the invention, including configurations where all LEDs in a LED set are not all coupled together in series. A resistor 82 may be coupled between power supply input 50 and a plurality of LEDs, for example LEDs 80 a-80 g, that may be connected in series in layer 22. LED 80 g may also be coupled to layer interconnection element 60, which may be coupled to return path 80 in interconnection layer 24 to allow a current to flow from power supply input 50 through LEDs 80 a-80 g, through return path 80 to power supply return 114. Other LED sets in light engine 10 may have the same or different configurations depending on the particular application.

Another embodiment of a LED set layout in light engine 200 is illustrated in FIG. 4. Light engine 200 may have a substrate 202, which may be a multi-layer metal core printed circuit board, and may have a first interconnection layer 204. Power supply inputs 250 a and 250 b may be configured to run adjacent to two edges of substrate 202 in layer 204. A plurality of LEDs may be mounted between power supply inputs 250 a and 250 b in a variety of configurations. For example, LEDs may be mounted in layer 204 in to parallel rows, parallel columns, diagonally, or in another arrangement. LED sets may be constructed by interconnecting LEDs from each row in an alternating pattern along the length of the rows. For example, a LED set may be constructed by coupling resistor 208 to power supply input 250 a, coupling LEDs 206 a-206 g together in series, coupling LED 206 g to layer interconnection element 210, and coupling layer interconnection element 210 to a return path (not shown) on another layer (not shown) of substrate 202. Similarly, another LED set may be constructed by coupling resistor 212 between power supply input 250 b, coupling resistor 212 to LEDs 216 a-216 g in series, and coupling LED 216 g to layer interconnection element 214. Layer interconnection element 214 may than be connected to a return path (not shown) to complete the circuit.

Light engine 200 may have additional LED sets (not shown) to form a plurality of LED groups. The LED sets in each LED group may be connected to a separate return path (not shown) associated with each LED group to allow each LED group to be controlled independently. In this configuration, power supply inputs 250 a and 250 b and return paths should be of a sufficient width to adequately handle the expected current, which may limit the width W of light engine 200. It may be desirable to design light engine 200 so that the length L is much greater than the width W so light engine 200 may approximate the dimensions of a fluorescent tube so that existing fluorescent encasements may be more readily modified for use with light engine 200. For example, the length L of light engine 200 may be at least ten times the width W. Similarly, it may be desirable to construct light engine 200 to have a narrow width of less than or equal to, for example, 1 or 2 inches.

It should be noted that the traces to implement power supply input 50 and return paths 80, 82, 84, and 86 of light engine 10 should be of a sufficient width to accommodate the expected current. For light engines having a large number of LEDs the width of the power supply input 50 and return paths 80, 82, 84, and 86 may limit the dimensions of the light engine and number of LEDs that may be mounted in a particular area. Employing a multi-layer metal core PCB may allow long and narrow light engines to be designed having a large number of LEDs because a second layer may be used for the return paths, allowing more space for power supply inputs and LEDs on a first layer. Moreover, the use of a MCPCB may allow a greater density of LEDs to be mounted to the light engine because MCPCBs have favourable thermal conduction properties.

A simplified schematic diagram of an embodiment of lighting apparatus 100 is illustrated in FIGS. 5 and 6. Lighting apparatus 100 may have a power supply 110 having a power supply output 112 and power supply return 114 coupled to control unit 120. Power supply 110 may be a constant voltage power supply or alternatively a constant current power supply in certain embodiments. Control unit 120 may be coupled to light engine 10 using mated connectors 124 of control unit 120 and connector 126 of light engine 10. The mated connectors may be connected together to allow power supply input 50, which may be coupled to power supply output 112 to be provided to light engine 10. The connectors may be chosen so that they may be physically connected and designed to minimize the space between control unit 120, light engine 10, and light engine 310 so that these components provide a more uniform light output and minimize any “dark” spots between light engines and provide a compact footprint for the lighting apparatus.

Connector 124 of control unit 120 may be a female connector adapted to be physically connected with male connector 126 of light engine 10. Connector 128 of light engine 10 may be a female connector adapted to be physically connected to male connector 130 of light engine 310. Such an arrangement allows either of light engines 10 or 310 to be physically connected to control unit 120 using connectors 126 or 130 and allows other light engines to be physically connected to light engines 10 or 310. This may increase the modularity of a lighting apparatus comprising light engines 10 and 310. In one embodiment, female connectors may be model no. 20-9159-005-101-116 or 22-9159-005-101-116 connectors and male connectors may be model no. 10-9159-005-101-116 connectors from AVX Corporation of South Carolina, U.S.A.

Similarly, connectors 124 and 126 may couple return paths 80, 82, 84, and 86 between light engine 10 and control unit 10 to provide a conductive path for each return path to power supply return 114. Light engine 10 may also have a connector 128 adapted to connect to connector 130 of light engine 310 so that power supply input 50 and return paths 80, 82, 84, and 86 may be coupled between light engines 10 and 310. Light engine 310 may also have a connector 132 that may be coupled to another light engine (not shown) in a similar fashion to maintain connectivity of power supply input 50 and return paths 80, 82, 84, and 86 between the various light engines. Additionally, more than three light engines may be coupled together in series and controlled by control unit 120. The coupling together of light engines in a modular fashion to be controlled by control unit 120 may increase the flexibility and decrease the cost of modifying lighting apparatus 100 for a particular application. For example, the modular design may reduce the number of SKUs of a manufacturer, which may simplify operations and reduce costs.

Light engines 10 and 310 may have the same or different configurations of LED groups and sets. Light engines 10 and 310 may be configured to have the same LED groups coupled to the same return path so that the LED groups on both of light engines 10 and 310 may be simultaneously controlled by control unit 120. Alternatively, other configurations of LED sets and LED groups may be employed in certain applications, noting that the control unit may be limited to simultaneously controlling LED sets coupled to each separate return path. Although four return paths are shown in FIG. 5, any other number of return paths may be used, for example, eight return paths may be used in certain applications. In certain embodiments, it may be possible to include four return paths in a light engine having a width of one inch and eight return paths in a light engine having a width of 1.75 inches.

One possible embodiment of control unit 120 is shown in FIG. 6 with details of the connectors omitted. Control unit 120 may be configured to couple power supply output 112 to power supply input 50 of light engine 10 to provide a source of power to light engine 10 and other light engines that may be coupled to light engine 10. Control unit 120 may also have a controller 126 connected to switching elements 128, 132, 134, and 136 so that controller 126 may selectively activate and deactivate each switching element to allow a current to flow from power supply output 112, through light engines 10 and 310, and back to power supply return 114. More specifically, switching element 128 may be coupled to activation output 130 of controller 126 so that a signal may be provided from controller 126 to selectively activate switching element 128 to allow a current to flow through return path 80. Switching elements 132, 134, and 136 may be configured in a similar manner to selectively allow current to flow through return paths 82, 84, and 86 respectively under the control of controller 126.

Switching element 128 may be implemented as a NMOS transistor having its gate coupled to activation output 130, its drain coupled to return path 80, and its source coupled to power supply return 114. When activation output 130 is set to high, the NMOS transistor may allow a current to flow from drain to source and similarly prevent a current from flowing when activation output is set to low in a known manner.

Control unit 120 may selectively activate all LED sets connected to each return path independently in this configuration. In embodiments where all LED sets in a particular LED group are all connected to the same return path, each LED group may be controlled independently by control unit 120. This may allow control unit 120 to provide a separate pulse width modulated (PWM) signal to each LED group. The ability to provide a separate PWM signal to each LED group may reduce the load on the power supply as certain algorithms may be used by controller 126 to minimize the current variation by staggering the PWM signal provided to each LED group compared to simultaneously turning on and off all LED groups at once. One possible algorithm to reduce the variation of the current supplied by power supply 110, where power supply 110 is a constant voltage power supply, is described in U.S. patent application Ser. No. 12/624,414 to Briggs which was published May 27, 2010 as U.S. Patent Application Publication No. 2010/0127632, which is incorporated by reference.

The ability to independently control LED groups may provide a number of advantages. For example, light engine 200 may have at least one LED set having a different colour or colour temperature from the remaining LED sets. For example, LEDs 206 a-206 g of a first LED set may be a first colour and LEDs 216 a-216 g of a second LED set may be a second colour. These LED sets may be included in different LED groups and be controlled separately so that the colour or colour temperature emitted by light engine 200 may be varied by control unit 120. For example, control unit 120 may control one LED group so that it has an increased duty cycle to increase the relative intensity of a particular spectrum of light being emitted by light engine 200. Alternatively, the PWM signals applied to each LED group may be offset to adjust the light output from light engine 200.

In certain embodiments at least one LED from at least two different LED groups may be mounted on light engine 10 or light engine 200 to be adjacent to or in close proximity to each other. More specifically, at least one LED from at least two different LED groups may be mounted so that the light radiated from these LEDs at least partially overlaps before the emitted light reaches optics (not shown) in a lighting apparatus. The lighting apparatus may also be constructed with particular optics to optimize the mixing of light having different colours or colour temperatures according to methods known in the art. This may allow for a more uniform light output from the lighting apparatus while allowing mixing of the emitted light where all or a subset of LEDs from at least two different LED groups have different colours or colour temperatures. For example, with reference to FIG. 4, LED 206 a from a first LED group may be mounted adjacent to or in close proximity to LEDs 216 a and 216 b of a second LED group so that the light emitted from LED 206 a at least partially overlaps with the light emitted from LEDs 216 a and 216 b. Similarly, it may be advantageous to intertwine individual LEDs of different LED groups and sets as shown in FIG. 4, where LEDs in each LED set are coupled together from alternating rows, to optimize the quality of light output from light engine 200 when the colour, colour temperature, or other parameters are adjusted.

Alternatively, in certain embodiments of the invention, control unit 120 may be omitted and replaced with pass through board 160. In these embodiments, LED groups may not be controlled independently and are simply provided with the signal from power supply output 112. Power supply 110 may provide a continuous power output or in certain embodiments be a switching power supply operable to provide a PWM signal. Pass through board 160 may be coupled to power supply 110 using connector 162 and light engine 10 using connector 164 so that power supply output 112 may be coupled to power supply input 50 of light engine 10. Connector 164 may also facilitate the coupling of return paths 80, 82, 84, and 86 from light engine 10 to power supply return 114 via connector 162. Return paths 80, 82, 84, and 86 may be coupled together on pass through board 160 so that a single return path is provided to power supply return 114. Pass through board 160 may allow a lighting apparatus to be constructed in a modular fashion and allows the same light engine architecture to be used for applications that require a control unit and those that do not require control. This may reduce costs and simplify the manufacturing process.

Alternatively, a lighting apparatus may be constructed having the functionality of control unit 120 or pass through board 160 on the same substrate as a light engine. Such a light engine may or may not be adapted to be coupled together with another light engine and be controlled by the controller mounted to the first light engine. This modified architecture maintains a degree of modular architecture and may simplify the manufacturing process and reduce costs in a similar fashion to that noted above.

A further alternative embodiment, may have control unit 120 located in a remote location or elsewhere in the encasement of a lighting apparatus and connected to at least one light engine via a cable rather than being physically connected to one end of a light engine as shown in FIG. 5. For example, control unit 120 may be located below the light engine or elsewhere in certain embodiments of a lighting apparatus. The control unit may continue to be able to control a plurality of light engines that may be coupled together as shown in FIG. 5 in a similar manner.

Another embodiment of the invention may include switching elements that may be controlled by controller 126, between power supply output 112 and the LED groups of light engine 10, instead of having the switching elements coupled between the return paths and the power supply return 114. In this embodiment, separate power supply inputs would be provided to the LED sets of each LED group and all LED sets may share a common return path or use a plurality of return paths. For example, the control unit illustrated in FIG. 6 could be modified to use the power supply input 50 as a return path that would be connected to power supply return 114 rather than power supply output 112. Similarly, return paths 80, 82, 84, and 86 may be used as power supply inputs to each LED group and be coupled to power supply output 112 instead of power supply return 114. Switching elements may be modified to use PMOS transistors connected between the power supply output 112 and LED groups, with a suitable voltage divider controlled by a transistor coupled to the gate of each PMOS transistor, so that each PMOS transistor may selectively allow a current to flow through each switching elements depending on the output of an activation output of controller 126 in a known manner. Such a configuration using a second layer to provide power inputs to each LED group may similarly allow a high density of LEDs to be mounted to a light engine.

Moreover, it should be noted that further configurations of the control unit may be utilized provided each LED group may be independently controlled by the control unit without departing from the scope of the invention.

When introducing elements of the present invention or the embodiments thereof, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

Of course, the above described embodiments are intended to be illustrative only and in no way limiting. The described embodiments of carrying out the invention are susceptible to many modifications of form, arrangement of arts, details and order of operation. The invention, rather, is intended to encompass all such modification within its scope, as defined by the claims. 

What is claimed is:
 1. A lighting apparatus comprising: a light engine comprising: a printed circuit board; and a plurality of LED groups on said printed circuit board coupled between a power supply input and a respective one of a plurality of return paths associated with said LED group; each of said LED groups comprising at least one LED set comprising a plurality of LEDs coupled in series; wherein a first one of said LED groups is comprised of at least a subset of LEDs having a first colour temperature, and a second one of said LED groups is comprised of at least a subset of LEDs having a second colour temperature different from said first colour temperature; and a control unit coupled between said light engine and a power source having a power supply output coupled to said power supply input of said light engine and a power supply return; wherein said control unit comprises: a plurality of transistors, one of said plurality of transistors coupled between each of said return paths and said power supply return; and a controller operable to selectively activate each of said transistors to allow current to flow from said power supply output through said associated LED group to said power supply return.
 2. The lighting apparatus of claim 1, wherein each of said LED groups comprises a plurality of LED sets coupled in parallel.
 3. The lighting apparatus of claim 2, wherein said printed circuit board comprises first and second interconnection layers; and wherein said plurality of LED sets of said LED groups are coupled in said first interconnection layer and are coupled to a respective one of said plurality of return paths associated with said LED group in said second interconnection layer.
 4. The lighting apparatus of claim 3, wherein each of said plurality of LED groups are coupled between said power supply input and a plurality of layer interconnection elements in said first interconnection layer; said layer interconnection elements are coupled to said return path associated with said LED group.
 5. The lighting apparatus of claim 1, wherein at least one of said LEDs having a first colour temperature from said first LED group and at least one of said LEDs having a second colour from said second LED group are intertwined on said light engine.
 6. The lighting apparatus of claim 1, wherein at least one of said LEDs having a first colour temperature from said first LED group and at least one of said LEDs having a second colour temperature from said second LED group are mounted so that the light emitted from said LEDs overlaps before reaching an optics section of said lighting apparatus.
 7. The lighting apparatus of claim 1, wherein said control unit implemented on a separate printed circuit board having a connector adapted to be physically connected to a first connector of said light engine.
 8. The lighting apparatus of claim 1 further comprising said power source comprising said power supply output coupled to said power supply input of said light engine and said power supply return coupled to said plurality of transistors.
 9. A lighting apparatus comprising: a plurality of light engines, each of said light engines comprising: a printed circuit board; and a plurality of LED groups on said printed circuit board coupled between a power supply input and a respective one of a plurality of return paths associated with said LED group across said plurality of light engines; each of said LED groups comprising at least one LED set comprising a plurality of LEDs coupled in series; wherein a first one of said LED groups is comprised of at least a subset of LEDs having a first colour temperature, and a second one of said LED groups is comprised of at least a subset of LEDs having a second colour temperature different from said first colour temperature; and a control unit coupled between said plurality of light engines and a power source having a power supply output coupled to said power supply inputs of each of said light engines and a power supply return; wherein said control unit comprises: a plurality of transistors, one of said plurality of transistors coupled between each of said return paths and said power supply return; and a controller operable to selectively activate each of said transistors to allow current to flow from said power supply output through said associated LED group on each of said plurality of light engines to said power supply return.
 10. The lighting apparatus of claim 9, wherein said return paths within at least one of said light engines are coupled to said transistors within said control unit via said return paths of another one of said light engines.
 11. The lighting apparatus of claim 9, wherein each of said LED groups comprises a plurality of LED sets coupled in parallel on each of said plurality of light engines.
 12. The lighting apparatus of claim 9, wherein said printed circuit boards of said plurality of light engines each comprise first and second interconnection layers; and wherein said plurality of LED groups are coupled in said first interconnection layer on each of said light engines and coupled to a respective one of a plurality of return paths associated with said LED group in said second interconnection layer of each of said light engines.
 13. The lighting apparatus of claim 9, wherein, in each of said light engines, at least one of said LEDs having a first colour temperature from said first LED group and at least one of said LEDs having a second colour from said second LED group are intertwined on said light engine.
 14. The lighting apparatus of claim 9, wherein, in each of said light engines, at least one of said LEDs having a first colour temperature from said first LED group and at least one of said LEDs having a second colour temperature from said second LED group are mounted so that the light emitted from said LEDs overlaps before reaching an optics section of said lighting apparatus.
 15. The lighting apparatus of claim 9, wherein said control unit implemented on a separate printed circuit board having a connector adapted to be physically connected to a first connector of each of said light engines.
 16. The lighting apparatus of claim 9 further comprising said power source comprising said power supply output coupled to said power supply input of each of said light engines and said power supply return coupled to said plurality of transistors.
 17. A control unit, adapted to be coupled to a light engine comprising a plurality of LED groups coupled between a power supply input and a respective one of a plurality of return paths associated with said LED group; wherein a first one of said LED groups is comprised of at least a subset of LEDs having a first colour temperature, and a second one of said LED groups is comprised of at least a subset of LEDs having a second colour temperature different from said first colour temperature; said controller comprising: a plurality of transistors; one of said plurality of transistors coupled between each of said return paths and a power supply return of a power source; and a controller, coupled to said transistors, operable to selectively activate each of said transistors to allow current to flow from said power supply input through said associated LED group to said power supply return.
 18. The control unit of claim 17 further comprising a connector adapted to be physically connected to a connector of said light engine.
 19. The control unit of claim 17 further comprising said power source comprising said power supply output adapted to be coupled to said power supply input of said light engine and said power supply return coupled to said plurality of transistors.
 20. A lighting apparatus incorporating said control unit of claim 17 and said light engine coupled to said control unit, wherein said control unit is operable to control light output from said light engine. 